Continuous measurement of yarn twist

Abstract

A method and apparatus for non-destructively measuring twist in a translating yarn (2) by means of a blade (1) which is in rubbing contact with the translating yarn (2) so that vibrations are imparted to the blade (1). The frequency of vibration of the blade (1) provides a measure of the twist imparted to the yarn (2) so that the signal frequency can be used as a measurement of the twist in a yarn (2) under test or as a feedback signal controlling the rate of twist imparted by a twist insertion station(8) during the formation of a yarn.

We claim: 
     
       1. A method of measuring twist in a translating yarn comprising sensing the frequency of vibration of a fixed blade having an edge in contact with the translating yarn and calculating the twist of the yarn which is a function of the frequency of vibration of said blade. 
     
     
       2. A method as claimed in claim 1 wherein the edge of the blade in contact with the yarn is perpendicular to the axis of the yarn where the yarn contacts the blade. 
     
     
       3. A method as claimed in claim 1 wherein the edge of the blade in contact with the yarn is inclined to the axis of the yarn where the yarn contacts the blade, said inclination being such that the amplitude of vibration of the blade, as the yarn is translating, is at a maximum. 
     
     
       4. Apparatus for measuring twist in a translating yarn comprising a fixed blade adapted to have an edge in contact with a translating yarn, means for sensing the vibration imparted to said blade by the translation of said yarn across said edge, and means for measuring the frequency of said vibration. 
     
     
       5. Apparatus as claimed in claim 4 wherein the means for sensing vibration of the blade comprise strain gauges located on opposite sides of the blade. 
     
     
       6. Apparatus as claimed in claim 4 wherein the means for sensing vibration of the blade comprises a piezo electric bimorph. 
     
     
       7. Apparatus as claimed in claim 4 where the output of the sensing means is input to a converter which produces an output proportional to the twist of the translating yarn. 
     
     
       8. Apparatus as claimed in claim 7 where the output of the converter is proportional to the instantaneous twist of the yarn. 
     
     
       9. Apparatus as claimed in claim 7 where the output of the converter is proportional to the average twist of the yarn for predetermined time intervals or lengths of yarn as the yarn is travelling in contact with the edge of the blade. 
     
     
       10. An automatic control system for a twist insertion apparatus comprising: a fixed blade adapted to have an edge in contact with a translating yarn; means for sensing the vibration imparted to said blade by the translation of said yarn across said edge; means for measuring the frequency of said vibration; and, means for providing a feedback signal controlling the twist insertion rate applied to input fibre material at a twist insertion station.